This Sunday the Gospel is the story of the Good Samaritan. Father Gabriel of St Mary Magdalen OCD gives a lead in which I think helps to see the relationship between the various Propers when he says:
"The unfortunate man represents each one of us. We too have encountered robbers on our way. The world, the devil and our passions have stripped and wounded us..."
Through sin, we lie beaten on the road, in need of help, as the Introit (from Psalm 69) requests:
"INCLINE unto my aid O God: "O Lord, make haste to help me: let my enemies be confounded and ashamed, who seek my soul. Ps. Let them be turned backward and blush for shame, who desire evils to me."
The Alleluia and Offertory both focus on the idea that we must acknowledge our own guilt, and plead with God to spare as. The latter takes its text from Exodus:
"Moses prayed in the sight of the Lord his God, and said: Why, O Lord, is Thy indignation enkindled against Thy people? Let the anger of Thy mind cease; remember Abraham, Isaac and Jacob, to whom Thou didst swear to give a land flowing with milk and honey: and the Lord was appeased from doing the evil which He had spoken of doing against His people."
Similarly, the Secret focuses on obtaining pardon from our sins through the sacrifice of the Mass.
Jesus, of course, is the Good Samaritan who binds up our wounds, pours on oil and wine, and carries us to the inn to recover. The Epistle (from 2 Corinthians 3) picks up this idea, pointing to our own sufficiency and the overwhelming glory of God. It also touches on the literal meaning of the Gospel, with its warning to follow the spirit of the law, not just the letter.
The link between Christ's add in bringing us to joy and the sacrifice being offered is most clearly brought out in the communio, which says:
"The earth shall be filled with the fruit of Thy works, O Lord, that Thou mayest bring bread out of the earth, and that wine may cheer the heart of man: that he may make the face cheerful with oil; and that bread may strengthen man’s heart."